Liquid crystal displays continue to be a dominant technology for flat panel displays. Liquid crystal displays that do not use polarizers, are reflective, and have intrinsic display memory are desirable in many situations. A number of reflective cholesteric liquid crystal displays has recently been developed. But these conventional reflective cholesteric liquid crystal displays typically suffer from one or more of the following deficiencies: switching between two states (e.g., planar state and focal-conic state) where one or both states are not stable under zero electric field; difficulty in fabricating black and white displays since one of the states must be colored (i.e., a color other than white or black); viewing angle dependency; poor light reflectivity; and poor contrast between the two states. There is a need, addressed by the present invention, to minimize or avoid one or more of above described problems.
The following documents may be relevant to the present invention:
Yang et al., U.S. Pat. No. 6,061,107.
Tamaoki et al., U.S. Pat. No. 6,103,431.
Yang et al., U.S. Pat. No. 5,847,798.
Doane et al., U.S. Pat. No. 5,691,795.
Wu et al., U.S. Pat. No. 5,625,477.
Wu et al., U.S. Pat. No. 5,661,533.
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H. Yuan, xe2x80x9cBistable Reflective Cholesteric Displays,xe2x80x9d Liquid Crystals in Complex Geometries Formed by polymer and porous networks, pp. 265-280 (Published by Taylor and Francis Ltd. 1996).
J. Kim et al., xe2x80x9cWhite Reflective Displays from Polymer-Stabilized Cholesteric Textures,xe2x80x9d SID, p. 802-805 (1998).
D.-K. Yang et al., xe2x80x9cCholesteric liquid crystal/polymer dispersion for haze-free light shutters,xe2x80x9d Appl. Phys. Lett., Vol. 60, pp. 3102-3104 (June 1992).
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W. D. Cook, xe2x80x9cPhotopolymerization kinetics of dimethacrylates using the camphorquinone/amine initiator system,xe2x80x9d Polymer, Vol. 33, pp. 600-609 (1992).
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D.-K. Yang et al., xe2x80x9cControl of reflectivity and bistability in displays using cholesteric liquid crystals,xe2x80x9d J. Appl. Phys., Vol. 76, pp. 1331-1333 (1994).
E. Korenic et al., xe2x80x9cCholesteric Liquid Crystal Flakesxe2x80x94A New Form of Domain,xe2x80x9d LLE Review, Vol. 74, pp. 139-149 (1998).
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W. Schuddeboom et al., xe2x80x9cExcited-State Dipole Moments of Dual Fluorescent 4-(Dialkylamino)benzonitriles. Influence of Alkyl Chain Length and Effective Solvent Polarity,xe2x80x9d J. Phys. Chem., Vol. 96, pp. 10809-10819 (1992). The compound of formula 1-I described in the present application is disclosed in Schuddeboom et al.
The present invention is accomplished in embodiments by providing a device comprising:
a liquid crystal composition including a liquid crystal and a liquid crystal domain stabilizing compound, wherein the liquid crystal composition is switchable between a strongly scattering state of a first plurality of smaller liquid crystal domains that strongly scatters a predetermined light and a weakly scattering state of a second plurality of larger liquid crystal domains that weakly scatters the predetermined light; and
a liquid crystal containment structure defining a space for the liquid crystal composition.
In further embodiments, there is provided a method comprising:
providing a liquid crystal composition including a liquid crystal and a liquid crystal domain stabilizing compound, wherein the liquid crystal composition is switchable between a strongly scattering state of a first plurality of smaller liquid crystal domains that strongly scatters a predetermined light and a weakly scattering state of a second plurality of larger liquid crystal domains that weakly scatters the predetermined light;
changing the weakly scattering state to the strongly scattering state by applying a first electric field to yield an unstable state of a single liquid crystal domain and then reducing the first electric field to a strongly scattering state inducing level to yield the strongly scattering state; and
changing the strongly scattering state to the weakly scattering state by applying a second electric field weaker than the first electric field but stronger than the strongly scattering state inducing level.
In embodiments of the present invention, the liquid crystal in both the smaller liquid crystal domains and the larger liquid crystal domains possesses helical axes that are randomly oriented.
In embodiments, there is a liquid crystal composition comprising:
(a) a liquid crystal; and
(b) a polymerized liquid crystal domain stabilizing compound comprising a dipolar monomer and a non-dipolar monomer.
In embodiments, there is a process comprising:
(a) forming a composition including a dipolar monomer and a non-dipolar monomer and polymerizing the dipolar monomer and the non-dipolar monomer to result in a polymerized liquid crystal domain stabilizing compound; and
(b) adding a liquid crystal to the composition at any time such as before, during, or subsequent to the polymerizing the dipolar monomer and the non-dipolar monomer.
A liquid crystal composition comprising:
(a) a liquid crystal;
(b) a liquid crystal domain stabilizing compound; and
(c) a dispersant.
A device comprising:
a liquid crystal composition including a liquid crystal, a liquid crystal domain stabilizing compound, and a dispersant, wherein the liquid crystal composition is switchable between a strongly scattering state of a first plurality of smaller liquid crystal domains that strongly scatters a predetermined light and a weakly scattering state of a second plurality of larger liquid crystal domains that weakly scatters the predetermined light; and
a liquid crystal containment structure defining a space for the liquid crystal composition.